Mass Spectrometry Device

ABSTRACT

With regard to an object of the invention, in a tandem type mass spectrometry system including three stages of a QMS, sensitivity of a daughter ion decreases due to loss resulting from destabilization of the daughter ion or a decrease in daughter ion generation rate, and an improvement insensitivity of the daughter ion is a significant issue. To solve the above-mentioned problem, the invention provides a mass spectrometry system having means of decreasing a q value of a parent ion and not decreasing a fundamental vibration frequency of the parent ion. According to the means of the invention, the invention may have effects that amass number range of a daughter ion that may be stably transmitted is expanded, the number of vibrations of a parent ion is substantially the same as that in a first stage of the QMS, and generation efficiency of the daughter ion does not decrease and can be maintained.

TECHNICAL FIELD

The present invention relates to a mass spectrometry device using atandem type quadrupole mass spectrometer, and particularly relates to amass spectrometry device that requires high sensitivity in a case ofanalytical use for an in vivo sample, and the like.

BACKGROUND ART

In a quadrupole mass spectrometer (QMS) including at least four rod-likeelectrodes to which a direct current voltage U and a high frequencyvoltage Vcos(Ωt+Φ₀) are applied, stability of an ion trajectory passingthrough a high frequency electric field generated among the electrodesis determined in a stable transmission area based on stability parametervalues a and q illustrated in FIG. 3. The stability parameters a and qare expressed by the following Equations.

$\begin{matrix}\left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack & \; \\{a = \frac{8{eZU}}{\Omega^{2}m\; r_{0}^{2}}} & (1) \\\left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack & \; \\{q = \frac{4{eZV}}{\Omega^{2}m\; r_{0}^{2}}} & (2)\end{matrix}$

Here, a mass-to-charge ratio of a target ion is m/Z, r₀ denotes a halfvalue of a distance between rod-like electrodes facing each other, edenotes an elementary charge, U denotes a direct current voltage, and Vand Ω denote an amplitude and an angular vibration frequency of a highfrequency voltage.

Conventionally, in a tandem type mass spectrometry device includingthree stages of the QMS, in a first stage of the QMS (Q1), only an ionspecies having a specific mass-to-charge ratio m/z passes through Q1,and thus a voltage applied to an electrode is adjusted such that anoperating point corresponds to a point near an apex of the stabletransmission area as illustrated in FIG. 4a . In a second stage of theQMS (Q2), a specific ion species (parent ion) passing through Q1 isbroken by collision induced dissociation, or the like to generate adissociated ion (daughter ion). In this instance, in order to stablypass a daughter ion in a wide mass number range, the direct currentvoltage is set to U=0 and the same voltage Vcos(Ωt+Φ₀) as that in Q1 isapplied as the high frequency voltage among the voltages applied to theelectrodes in Q2 such that the operating point is on an a=0 axis, andthe q value is the same between Q1 and Q2 as illustrated in FIG. 4 a.

In addition, as described in JP 2012-516013 A, in the second stage ofthe QMS (Q2), the direct current voltage is set to U=0, the amplitude ofthe high frequency voltage Vcos(Ωt+Φ₀) is the same as that in the caseof Q1, and a frequency Ω/(2π) is set to be larger than or smaller than afrequency in Q1.

CITATION LIST Patent Literature

PTL 1: JP 2012-516013 A

SUMMARY OF INVENTION Technical Problem

In a tandem type mass spectrometry device including three stages of theQMS, a mass of a parent ion is selected and separated in a first stageof the QMS (Q1), the parent ion is dissociated to generate and stablytransmit a daughter ion in a second stage of the QMS (Q2), and massspectrum analysis is performed on various daughter ions in a third stageof the QMS (Q3).

Conventionally, as illustrated in FIG. 4a , in Q1, only an ion specieshaving a specific mass-to-charge ratio m/z passes through Q1, and thus avoltage applied to an electrode is adjusted such that an operating pointcorresponds to a point near an apex of the stable transmission area. InQ2, in order to stably pass a daughter ion generated by breaking aparent ion passing through Q1, only a direct current voltage is changedto U=0, and a high frequency voltage is not changed such that anoperating point is on an a=0 axis. In this instance, as illustrated inFIG. 4a , since a value of a stability parameter q of the parent ion isalmost unchanged, the daughter ion generated by dissociating the parention has a lower mass number than that of the parent ion, and thus m/Zbecomes smaller. As a result, as illustrated in Equation (2), a q valueof the daughter ion is larger than a q value of the parent ion, somedaughter ions come out of the stable area, and there is a possibilitythat stable transmission (detection) will not be allowed, andsensitivity will decrease.

In addition, as described in JP 2012-516013 A, in the second stage ofthe QMS (Q2), when the direct current voltage is set to U=0, and theamplitude V is the same as that in the case of Q1 and the frequencyΩ/(2π) is larger than the frequency of Q1 with regard to the highfrequency voltage Vcos(Ωt+Φ₀), the q value of the parent ion decreases,and the q value of the daughter ion decreases as illustrated in FIG. 4b, and thus a mass number range of a daughter ion that may be stablytransmitted increases. However, when the q value of the parent ion ismerely decreased, a fundamental vibration frequency (Equation (3)) ofthe parent ion decreases as illustrated in FIG. 5a .

$\begin{matrix}\left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack & \; \\{{\omega \approx \frac{q\; \Omega}{2\sqrt{2}}} = \frac{\sqrt{2}{eZV}}{m\; r_{0}^{2}\Omega}} & (3)\end{matrix}$

In this instance, when the fundamental vibration frequency of the parention decreases, in particular, when the parent ion is dissociated by aCID, the number of collisions with buffer gas such as neutral gasdecreases. Therefore, since dissociation efficiency of the parent ion,that is, a generation rate of the daughter ion is reduced, there is apossibility that sensitivity of the daughter ion may be reduced.

That is, in the conventional method, two problems below are considered.

(1) Decrease in sensitivity due to an unstable trajectory of thedaughter ion (coming out of the stable area)

(2) Decrease in sensitivity due to a decrease in generation efficiencyof the daughter ion (a decrease in the number of vibrations of theparent ion)

To solve the above-described problems, means of not decreasing thefundamental vibration frequency of the parent ion while decreasing the qvalue of the parent ion is required.

Solution to Problem

In the invention, in a tandem type quadrupole mass spectrometry system,as means of not decreasing a fundamental vibration frequency of a parention while decreasing a q value of the parent ion in order to solve theabove-described problems, when a q value of the parent ion in Q1 is setto q1, a q value of the parent ion in Q2 is set to q2, and fundamentalvibration frequencies of the parent ion in Q1 and Q2 are set to ω1 andω2,

$\begin{matrix}\left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack & \; \\{q_{2} = {\frac{1}{\gamma}q_{1}\mspace{14mu} \left( {Y > 1} \right)}} & (4) \\\left\lbrack {{Equation}\mspace{14mu} 5} \right\rbrack & \; \\{\omega_{2} = \omega_{1}} & (5) \\\left\lbrack {{Equation}\mspace{14mu} 6} \right\rbrack & \; \\{\Omega_{2} = {\gamma \cdot {\Omega_{1}\left( {Y > 1} \right)}}} & (6)\end{matrix}$

Here, in order to satisfy both Equations (4) and (5), Equation (6) needsto be satisfied. Therefore, in order to satisfy Equations (4) to (6),applied voltages (a direct current voltage U and a high frequencyvoltage Vcos(Ωt)) of Q1 and Q2 are controlled, and a distance betweenelectrodes of Q1 and Q2 is changed such that the following Equation issatisfied.

$\begin{matrix}\left\lbrack {{Equation}\mspace{14mu} 7} \right\rbrack & \; \\{\frac{V_{1}}{r_{0_{1}}^{2}\Omega_{1}} = {\frac{V_{2}}{r_{0_{2}}^{2}\Omega_{2}}\left( {\Omega_{1} \neq \Omega_{2}} \right)}} & (7)\end{matrix}$

Effects that a mass number range of a daughter ion that may be stablytransmitted is expanded and generation efficiency of the daughter iondoes not decrease (the number of vibrations of the parent ion issubstantially the same as that in Q1) are considered to be expectable bythe means of the invention.

Advantageous Effects of Invention

As described above, effects that a mass number range of a daughter ionthat may be stably transmitted is expanded and generation efficiency ofthe daughter ion does not decrease (the number of vibrations of theparent ion is substantially the same as that in Q1) are considered to beexpectable in a tandem type quadrupole mass spectrometry system of theinvention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of arrangement of various electrodes and astructure of a tandem type quadrupole mass spectrometry device of afirst embodiment of the invention.

FIG. 2 is a schematic diagram of an entire mass spectrometry system formeasuring mass spectrometry data according to the invention.

FIG. 3 is a diagram of an ion stable transmission area in a quadrupoleelectric field.

FIG. 4 is a conceptual diagram of operating points in a first stage anda second stage of a QMS in a diagram of an ion stable transmission areaof a quadrupole mass spectrometer.

FIG. 5 is a conceptual diagram of a parent ion trajectory in the firststage and the second stage of the QMS.

FIG. 6 is a diagram summarizing a result of deriving a potentialdistribution of generated potentials and an ion destabilization losscumulative number by a simulation in the case of an ion guide andelectrode arrangement/shape of a mass spectrometer unit according to asecond embodiment of the invention.

FIG. 7 is a schematic diagram of arrangement of various electrodes and astructure of a tandem type quadrupole mass spectrometry device in thesecond embodiment of the invention.

FIG. 8 is a conceptual diagram of an operating point in a first stageand a second stage of a QMS in an ion stable transmission area diagramof a quadrupole mass spectrometer according to a third embodiment of theinvention.

FIG. 9 is a schematic diagram of arrangement of various electrodes and astructure of a tandem type quadrupole mass spectrometry device.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the invention will be described withreference to drawings.

First, a first embodiment will be described with reference to FIG. 1 toFIG. 5b . FIG. 1 is a diagram illustrating a tandem type quadrupole massspectrometry device including three stages of a QMS corresponding to acharacteristic of the first embodiment, and FIG. 2 is a block diagram ofan entire mass spectrometry system of the present embodiment. First, ananalysis flow is shown for a mass spectrometry system 11. A sample to bemass-analyzed is separated and fractionated in terms of time in apretreatment system 1 such as gas chromatography (GC) or liquidchromatography (LC), and sample ions successively ionized by anionization unit 2 are injected into a mass spectrometer unit 4 throughan ion transport unit 3 and mass-separated. Here, m is an ion mass and Zis a charge valence of an ion. A voltage to the mass separation unit 4is applied from a voltage source 9 while being controlled by acontroller 8. Finally, separated and passed ions are detected by an iondetector 5 and data-arranged/processed by a data processing unit 6, andmass spectrometry data corresponding to an analysis result thereof isdisplayed on a display unit 7. All this series of mass analysisprocesses (ionization of samples, transportation and incidence of asample ion beam to the mass spectrometer unit 3, a mass separationprocess, ion detection, data processing, and command processing of auser input unit 10) are controlled by the controller 8. Here, asillustrated in FIG. 1, the mass separation unit 4 is configured by threerows of a quadrupole mass spectrometers (QMS) including four rod-likeelectrodes substantially coaxially connected to one another. Here, amulti-pole mass spectrometer including four or more rod-like electrodesmay be used. In addition, as illustrated in FIG. 1, when a longitudinaldirection of the rod-like electrodes is set to a z direction, and asectional direction thereof is set to x and y planes, the four rod-likeelectrodes may correspond to cylindrical electrodes as illustrated inx-y cross sectional views of the rod-like electrodes or correspond torod-like electrodes having a bipolar surface shape indicated by a dottedline.

In four electrodes of an ith stage of the QMS in the mass spectrometerunit 4, when electrodes facing each other are regarded as one set, acomposite voltage of a direct current voltage and a high frequencyvoltage: +(U_(i)+VicosΩ_(i)t) is applied to electrodes 4-i-a and 4-i-c,and an opposite phase voltage thereof: −(U_(i)+VicosΩ_(i)t) is appliedto electrodes 4-i-b and 4-i-d. Further, high frequency electric fieldsE_(xi) and E_(yi) shown in Equation (8) are generated among the fourrod-like electrodes.

$\begin{matrix}\left\lbrack {{Equation}\mspace{14mu} 8} \right\rbrack & \; \\{{E_{x_{i}} = {{- \frac{\partial\Phi_{i}}{\partial x}} = {{- \frac{2\left( {U_{i} + {V_{i}\cos \; \Omega_{i}t}} \right)}{r_{0_{i}}^{2}}} \cdot x}}},{E_{y_{i}} = {{- \frac{\partial\Phi_{i}}{\partial y}} = {{+ \frac{2\left( {U_{i} + {V_{i}\cos \; \Omega_{i}t}} \right)}{r_{0_{i}}^{2}}} \cdot y}}}} & (8)\end{matrix}$

Here, i denotes an ordinal number in stages of the QMS. In this case,i=1 to 3 since the QMS has three stages. Ionized sample ions areintroduced along a central axis (z direction) between the rod-likeelectrodes and pass through the high frequency electric field ofEquation (8). Stability of the ion trajectory in x and y directions atthis time is determined based on non-dimensional parameters a_(i) andq_(i) below derived from an equation of motion (Mathieu equation) ofions between the rod-like electrodes.

$\begin{matrix}\left\lbrack {{Equation}\mspace{14mu} 9} \right\rbrack & \; \\{a_{i} = \frac{8{eZU}_{i}}{\Omega_{i}^{2}m\; r_{0_{i}}^{2}}} & (9) \\\left\lbrack {{Equation}\mspace{14mu} 10} \right\rbrack & \; \\{q_{i} = \frac{4{eZV}_{i}}{\Omega_{i}^{2}m\; r_{0_{i}}^{2}}} & (10)\end{matrix}$

Here, the non-dimensional parameters a_(i) and q_(i) correspond tostability parameters in the ith stage of the QMS. In addition, inEquations (9) and (10), r₀ denotes a half value of a distance betweenrod-like electrodes facing each other, e denotes an elementary charge,m/Z denotes a mass-to-charge ratio of an ion, U denotes a direct currentvoltage applied to the rod-like electrodes, and V and Ω denote anamplitude and an angular vibration frequency of a high frequencyvoltage. When values of r₀, U, V, and Ω are determined, respective ionspecies correspond to different points (a_(i), q_(i)) on an a-q plane ofFIG. 3 depending on mass-to-charge ratios m/Z thereof. In this instance,from Equations (9) and (10), all the different points (a_(i), q_(i)) ofthe respective ion species are present on a straight line of thefollowing Equation (11).

$\begin{matrix}\left\lbrack {{Equation}\mspace{14mu} 11} \right\rbrack & \; \\{a_{i} = {\frac{2U_{i}}{V_{i}}q_{i}}} & (11)\end{matrix}$

FIG. 3 illustrates a quantitative range (stable transmission area) ofa_(i) and q_(i) assigning a stable solution to ion trajectories in boththe x and y directions. In order to allow only ion species having aspecific mass-to-charge ratio m/Z to pass between the rod-likeelectrodes and cause unstable emission of the other ion species outsidethe QMS for mass separation, a U/V ratio needs to be adjusted tointersect a vicinity of an apex of the stable transmission area of FIG.3 (FIG. 3). Stably transmitting ions pass between the rod-likeelectrodes in a z direction while vibrating. On the other hand,vibrations of destabilization ions diverge and the destabilization ionsexit in the x and y directions. Using this point, in a tandem typequadrupole mass spectrometry system based on three stages of the QMS, inthe first stage of the QMS (Q1), in order to pass only an ion specieshaving a specific mass-to-charge ratio m/Z, a voltage applied to anelectrode is adjusted such that an operating point corresponds to apoint near the apex of the stable transmission area as illustrated inFIG. 4a . In the second stage of the QMS (Q2), a collision chamber 13filled with a buffer gas such as a neutral gas is installed, and aspecific ion species (parent ion) passing through Q1 is broken bycollision induced dissociation, or the like to generate a dissociatedion (daughter ion) therein. In the third stage of the QMS (Q3), variousdaughter ions are subjected to mass spectrum analysis.

In the present embodiment, voltages applied to each ith stage of the QMS(the direct current voltage U_(i) and the high frequency voltageV_(i)cosΩ_(i)t) are controlled as shown in control content 12 of FIG. 1.Referring to a voltage U_(l)+V_(l)cosΩ_(l)t applied to Q1, in order toallow only a certain parent ion to pass by mass separation, U₁, V₁, andω₁ are adjusted such that the parent ion corresponds to the apex of thestable area based on Equations (8) and (9) as illustrated in FIG. 4 b.

In Q2, as illustrated in FIG. 4b , the direct current voltage is set toU₂=0, and a control operation is performed based on Equation (7) suchthat the q value of the parent ion decreases when compared to the caseof Q1 and a fundamental vibration frequency ω₂ is substantially the sameas that in the case of Q1 (ω₁). However, in the present embodiment,since the half value r₀ of the distance between rod-like electrodes isthe same among Q1, Q2, and Q3, a control operation is performed toobtain Equation (12).

$\begin{matrix}\left\lbrack {{Equation}\mspace{14mu} 12} \right\rbrack & \; \\{\frac{V_{1}}{\Omega_{1}} = {\frac{V_{2}}{\Omega_{2}}\left( {\Omega_{1} \neq \Omega_{2}} \right)}} & (12)\end{matrix}$

That is, in order to set a value of V/Ω to be substantially the samebetween Q1 and Q2 and satisfy Equation (6),

[Equation 13]

V ₂ =γ·V ₁(y>1).   (13)

Further, an amplitude V₂ of a high frequency voltage V₂cosΩ2t applied toQ2 and a value of an angular vibration frequency Ω₂ are set and appliedbased on Equation (6) and Equation (13).

According to the present embodiment, effects that amass number range ofa daughter ion that may be stably transmitted is expanded, the number ofvibrations of a parent ion is substantially the same as that in Q1, andgeneration efficiency of the daughter ion does not decrease areconsidered to be expectable merely by adjusting voltages applied to Q1and Q2.

Next, a second embodiment will be described with reference to FIGS. 6and 7. Here, as illustrated in FIG. 6, in a rod-like electrode 15 of Q2,when a half value r₀₂ of a distance between rod-like electrodes has arelational expression below with respect to r₀₁ of Q1,

$\begin{matrix}\left\lbrack {{Equation}\mspace{14mu} 14} \right\rbrack & \; \\{r_{0_{2}} = {\frac{r_{0_{1}}}{\sqrt{\gamma}}\left( {Y > 1} \right)}} & (14)\end{matrix}$

With regard to a voltage applied to the second stage of the QMS (highfrequency voltage V₂cosΩ_(2t)), as illustrated in control content 14 ofFIG. 7,

[Equation 15]

V₂=V₁   (15)

A control operation is performed to satisfy Equation (6) and Equation(15). According to the present embodiment, since only an angularvibration frequency·2 of the high frequency voltage V₂cosΩ2t of Q2 maybe controlled, the same effect as that of the first embodiment isconsidered to be obtained by a relatively easy control operation.

Next, a third embodiment will be described with reference to FIG. 8.Here, a case where a parent ion is charged to be a multivalent ion(Z>1), and the like is presumed. In this case, a mass-to-charge ratiom/z of a daughter ion generated by dissociating the parent ion may notbe smaller than a mass-to-charge ratio m/z of the parent ion. Forexample, when a parent ion of a mass number 5,000 [Da] is charged to bea pentavalent ion, a mass-to-charge ratio is m/z=1,000. When amonovalent daughter ion of a mass number 2,000 [Da] is generated, amass-to-charge ratio becomes m/z=2,000 from the parent ion, and themass-to-charge ratio increases. When such daughter ion generation ispresumed, the q₂ value of the parent ion in Q2 is set to be larger thanthe q₁ value of the parent ion in the case of Q1 as illustrated in FIG.8. In this case, an applied voltage or a distance between electrodes ofQ2 may be controlled by substituting γ<1 into the control content 12 ofFIGS. 1 and 7. According to the present embodiment, the same effect asthat of the first and second embodiments is considered to be expectableeven when the parent ion is a multivalent ion, and the daughter ion hasa large mass-to-charge ratio.

Next, a fourth embodiment will be described with reference to FIG. 9.Here, based on mass spectrum data obtained by assigning a γ valuecorresponding to a control parameter within a certain range, an optimumvalue of the γ value is automatically derived and the applied voltage ofQ2 is automatically corrected to an optimum γ value. According to thepresent embodiment, since an optimum value of γ is systematicallyderived and set without inputting an optimum γ value by the user, it isconsidered that highly accurate analysis may be easily performed.

REFERENCE SIGNS LIST

-   1 pretreatment system-   2 ionization unit-   3 ion transport unit-   4 mass spectrometer unit-   5 ion detector-   6 data processing unit-   7 display unit-   8 controller-   9 voltage source-   10 user input unit-   11 entire tandem type mass spectrometry system-   12 applied voltage control content-   13 collision chamber-   14 applied voltage control content in second embodiment-   15 electrode of Q2 in second embodiment-   γ optimum value deriving unit

1. A mass spectrometry device, comprising: a mass spectrometer unitwhich includes at least four rod-like electrodes, applies a directcurrent voltage U and a high frequency voltage VcosΩt to the rod-likeelectrodes to generate a multi-pole field greater than or equal to aquadrupole field of a high frequency between the rod-like electrodes,and mass-selects/separates an ion species having a specificmass-to-charge ratio m/z; and a detector which detects an ion passingthrough the mass spectrometer unit, wherein at least two or more stagesof the mass spectrometer unit are coaxially provided in series, and avoltage applied to an electrode and a half value r₀ of a distancebetween electrodes of the mass spectrometer unit are controlled in afirst stage of the mass spectrometer unit and a second stage of the massspectrometer unit such that a fundamental vibration frequency of acertain ion species is substantially the same between the first stageand the second stage.
 2. The mass spectrometry device according to claim1, wherein at least three stages of the mass spectrometer unit areincluded, an ion species having a certain mass-to-charge ratio is passedin a first stage of the mass spectrometer unit, a dissociated ion isgenerated by collision induced dissociation with respect to a certainion passing through the first stage in a second stage of the massspectrometer unit, and the dissociated ion is mass-analyzed in a thirdstage of the mass spectrometer unit.
 3. The mass spectrometry deviceaccording to claim 1, wherein voltages applied to the electrodes or adistance between the rod-like electrode of the mass spectrometer unitare controlled in the first stage of the mass spectrometer unit and thesecond stage of the mass spectrometer unit such that a value of V/(r₀²Ω) is substantially the same between the first stage and the secondstage.
 4. The mass spectrometry device according to claim 1, whereinvoltages applied to the electrodes of the mass spectrometer unit arecontrolled in the first stage of the mass spectrometer unit and thesecond stage of the mass spectrometer unit such that a value of a ratioV/Ω of an amplitude value V of the high frequency voltage to an angularvibration frequency Ω of the high frequency voltage is substantially thesame between the first stage and the second stage.
 5. The massspectrometry device according to claim 1, wherein voltages applied tothe electrodes or a distance between the rod-like electrode of the massspectrometer unit are controlled such that a value of V/(r₀ ²Ω²) in thesecond stage of the mass spectrometer unit is smaller than a value ofV/(r₀ ²Ω²) in the first stage of the mass spectrometer unit by γ timeswith respect to the high frequency voltage VcosΩt applied to therod-like electrodes and the half value r₀ of the distance between therod-like electrodes.
 6. The mass spectrometry device according to claim1, wherein voltages applied to the electrodes or a distance between therod-like electrode of the mass spectrometer unit are controlled suchthat a value of V/(r₀ ²Ω²) in the second stage of the mass spectrometerunit is larger than a value of V/(r₀ ²Ω²) in the first stage of the massspectrometer unit by γ times with respect to the high frequency voltageVcosΩt applied to the rod-like electrodes and the half value r₀ of thedistance between the rod-like electrodes.
 7. The mass spectrometrydevice according to claim 1, wherein voltages applied to the electrodesof the mass spectrometer unit are controlled such that a value Ω in thesecond stage of the mass spectrometer unit is larger than a value Ω inthe first stage of the mass spectrometer unit by γ times with respect tothe high frequency voltage VcosΩt applied to the rod-like electrodes. 8.The mass spectrometry device according to claim 1, wherein voltagesapplied to the electrodes of the mass spectrometer unit are controlledsuch that a value Ω in the second stage of the mass spectrometer unit issmaller than a value Ω in the first stage of the mass spectrometer unitby γ times with respect to the high frequency voltage VcosΩt applied tothe rod-like electrodes.
 9. The mass spectrometry device according toclaim 5, wherein an optimum γ value from which an optimum analysisresult is obtained is automatically derived by assigning the γ valuewithin a certain range.
 10. A mass spectrometry device, comprising: amass spectrometer unit which includes at least four rod-like electrodes,applies a direct current voltage U and a high frequency voltage VcosΩtto the rod-like electrodes to generate a multi-pole field greater thanor equal to a quadrupole field of a high frequency between the rod-likeelectrodes, and mass-selects/separates an ion species having a specificmass-to-charge ratio m/z; and a detector which detects an ion passingthrough the mass spectrometer unit, wherein at least two or more stagesof the mass spectrometer unit are coaxially provided in series, and astability parameter of a first stage of the mass spectrometer unit isset to be γ times (γ>1) a stability parameter of a second stage of themass spectrometer unit, and an angular vibration frequency Ω₁ of thefirst stage of the mass spectrometer unit and an angular vibrationfrequency Ω₂ of the second stage of the mass spectrometer unit are setto satisfy a following relation:Ω₂=Ω₁·γ′, 1<γ′≤γ, (stability parameter)=4eZV/Ω²mr₀ ², where r₀ denotes ahalf value of a distance between rod-like electrodes facing each other,e denotes an elementary charge, V denotes an amplitude of a highfrequency voltage, and Ω denotes an angular vibration frequency.
 11. Themass spectrometry device according to claim 10, wherein the stabilityparameter is set by changing the distance between the rod-likeelectrodes.
 12. The mass spectrometry device according to claim 10,wherein the stability parameter is set by controlling voltages appliedto the rod-like electrodes.